BOSTON - The Celtics were all but buried.

The Indiana Pacers, massive underdogs in these Eastern Conference finals, coming off a dramatic victory over the New York Knicks at Madison Square Garden to advance to this series 48 hours earlier, had the ball and were up three with 10 seconds remaining. They only needed to inbound the ball and hit a free throw to seal the victory.

But then Indiana threw the ball away, giving the Celtics life. And after a spectacular inbounds pass from Jrue Holiday -- one of many spectacular moments from him en route to a 28-point, 7-rebound, 8-assist, 3-steal performance -- to Jaylen Brown in the corner allowed Brown to rise and fire from 3, he hit the game-tying jumper with 5.7 seconds remaining.

The shot ultimately sent Boston on its way to a heart-stopping 133-128 overtime victory to open this best-of-7 affair.

"It was a good momentum play that we were able to get a turnover," said Brown, who finished with 26 points, 7 rebounds, 5 assists and 3 steals in 44 minutes. "Jrue made a great pass. [Derrick] White set a great screen.

"And the rest was history."

This was the definition of a great escape from Boston, which was on the verge of dropping to an inexplicable 15-15 at TD Garden across the past three postseasons before Brown's game-saving shot and Indiana's multiple inexplicable miscues.

Boston was able to survive a game that saw Jayson Tatum go 2-for-10 from the field in the fourth quarter and overtime before hitting what wound up being the game-clinching buckets on back-to-back possessions -- an and-1 over T.J. McConnell and a 3-pointer from the top of the key -- to put the game away. Tatum ended up with 36 points and was a plus-20 on the night.

In addition, Boston had several ugly turnovers late, including one each by Brown and Tatum, while Indiana feasted on getting center Al Horford isolated in switches down the stretch. Both Pacers forward Pascal Siakam and guard Andrew Nembhard repeatedly got clean mid-range jumpers that they knocked down, helping Indiana to a 5-point lead with1:57 remaining in the fourth quarter.

At that point, Boston was in trouble, magnified by Tatum missing a couple of shots inside the final 40 seconds.

"We always knew that there's always a chance," Holiday said. "We've seen crazy stuff happen all the time. I don't think that we think we lost the game until we actually lost the game. And that's part of the reason why we were so resilient toward the end of the game.

"Like I said, anything can happen. A couple turnovers, a great shot, great look by JB or on the other end, we make a couple other shots that were wide open and it could be a completely different game. So just the type of team that's going to keep on fighting no matter how long and no matter what it takes."

After Boston opened the game with a 12-0 run, Indiana clawed back from an early deficit, taking its first lead to open the second half with five straight points from superstar guard Tyrese Haliburton. But a 26-8 run in response gave Boston a 13-point lead in the third quarter -- its largest of the contest.

Indiana, though, didn't play the part of a 9.5-point underdog, repeatedly fighting its way back into the game thanks to shooting 62.5 percent on 2-point shots after setting a new NBA record for field goal percentage in a postseason game in its Game 7 victory over the Knicks Sunday afternoon.

That stat, in particular, was a reminder of the absence of Kristaps Porzingis, who missed his seventh straight game with a calf strain. ESPN's Adrian Wojnarowski reported before the game that Porzingis could be back as soon as Game 4 in Indianapolis on Memorial Day.

"Nothing other than what I expected," Celtics coach Joe Mazzulla said when asked about how he thought the game played out. "Two high-level teams competing for a great opportunity. So I expect all the games to be like that, and there's going to be more of that. And I thought both teams competed at a high level. For us, I thought our guys, obviously we weren't perfect. We can get better. But I thought we maintained a level of poise, a level of mental toughness to just continue to work through some of the mistakes.

"That's the bind they put you in, because of the way they play. So we handled it well, and we need to get better."

The goal now for the Celtics is to find a way to do what they couldn't in the first two rounds of these playoffs: claim a victory in Game 2, and put a stranglehold on this series.

Even that directive feels a lot different after Boston managed to escape with the win in Game 1.

"Come with the mindset of don't relax," Tatum said, when asked how he'll approach Game 2 Thursday. "Different circumstances. The first two rounds we won our Game 1 by a wide margin, so maybe human nature played into that. But tonight being a close game, going into overtime, we certainly felt like we should have won and we could have played better.

"I'm excited for us to come out and respond and protect home court better than we have recently."